Tan Gao | 3768ffe | 2011-08-30 11:12:20 -0700 | [diff] [blame] | 1 | # Copyright (c) 2011 The Chromium OS Authors. All rights reserved. |
| 2 | # Use of this source code is governed by a BSD-style license that can be |
| 3 | # found in the LICENSE file. |
| 4 | |
| 5 | """A base class to interact with I2C slave device. |
| 6 | |
| 7 | Dependency |
| 8 | - This library depends on a new C shared library called "libsmogcheck.so". |
| 9 | """ |
| 10 | |
| 11 | import ctypes, logging |
| 12 | |
| 13 | |
| 14 | # I2C constants |
| 15 | I2C_BUS = 2 |
| 16 | |
| 17 | # Path of shared library. |
| 18 | SMOGCHECK_C_LIB = "/usr/local/lib/libsmogcheck.so.0" |
| 19 | |
| 20 | |
| 21 | class I2cError(Exception): |
| 22 | """Base class for all errors in this module.""" |
| 23 | |
| 24 | |
| 25 | class I2cSlave(object): |
| 26 | """A generic I2C slave object that supports basic I2C bus input/output.""" |
| 27 | |
| 28 | def __init__(self, adapter_nr=None, load_lib=None): |
| 29 | """Constructor. |
| 30 | |
| 31 | Mandatory params: |
| 32 | adapter_nr: adapter's number address. Default: I2C_BUS. |
| 33 | fd: file descriptor to communicate with I2C bus. |
| 34 | lib_obj: ctypes library object to interface with SMOGCHECK_C_LIB. |
| 35 | load_lib: a string, name of C shared library object to load. |
| 36 | slave_addr: slave address to set. Default: None. |
| 37 | |
| 38 | Args: |
| 39 | lib: a string, name of C shared library object to load. |
| 40 | """ |
| 41 | self.slave_addr = None |
| 42 | |
| 43 | if adapter_nr is None: |
| 44 | adapter_nr = I2C_BUS |
| 45 | self.adapter_nr = adapter_nr |
| 46 | |
| 47 | if load_lib is None: |
| 48 | load_lib = SMOGCHECK_C_LIB |
| 49 | self.load_lib = load_lib |
| 50 | |
| 51 | # Load shared library object. |
| 52 | self.lib_obj = self._loadSharedLibrary() |
| 53 | self.fd = self._getDeviceFile() |
| 54 | |
| 55 | def _loadSharedLibrary(self): |
| 56 | """Loads C shared library .so file. |
| 57 | |
| 58 | Returns: |
| 59 | a new instance of the shared (C) library. |
| 60 | |
| 61 | Raises: |
| 62 | I2cError: if error loading the shared library. |
| 63 | """ |
| 64 | logging.info('Attempt to load shared library %s', self.load_lib) |
| 65 | try: |
| 66 | return ctypes.cdll.LoadLibrary(self.load_lib) |
| 67 | except OSError, e: |
| 68 | raise I2cError('Error loading C library %s: %s' % |
| 69 | (self.load_lib, e)) |
| 70 | logging.info('Successfully loaded shared library %s', self.load_lib) |
| 71 | |
| 72 | def _getDeviceFile(self): |
| 73 | """Gets a file descriptor of a device file. |
| 74 | |
| 75 | Returns: |
| 76 | fd: an integer, file descriptor to communicate with I2C bus. |
| 77 | |
| 78 | Raises: |
| 79 | I2cError: if error getting device file. |
| 80 | """ |
| 81 | logging.info('Attempt to get device file for adapter %s', |
| 82 | self.adapter_nr) |
| 83 | fd = self.lib_obj.GetDeviceFile(self.adapter_nr) |
| 84 | if fd < 0: |
| 85 | raise I2cError('Error getting device file for adapter %s' % |
| 86 | self.adapter_nr) |
| 87 | |
| 88 | logging.info('Got device file for adapter %s', self.adapter_nr) |
| 89 | return fd |
| 90 | |
| 91 | def setSlaveAddress(self, addr): |
| 92 | """Sets slave address on I2C bus to be communicated with. |
| 93 | |
| 94 | TODO(tgao): add retry loop and raise error if all retries fail. |
| 95 | (so that caller does not have to check self.err for status) |
| 96 | |
| 97 | We use 7-bit address space for I2C, which has 128 addresses total. |
| 98 | Besides 16 reserved addresses, the total usable address space is 112. |
| 99 | See - http://www.i2c-bus.org/addressing/ |
| 100 | |
| 101 | Args: |
| 102 | addr: a (positive) integer, 7-bit I2C slave address. |
| 103 | |
| 104 | Raises: |
| 105 | I2cError: if slave address is invalid or can't be set. |
| 106 | """ |
| 107 | if self.slave_addr == addr: |
| 108 | logging.info('Slave address already set, noop: %s', addr) |
| 109 | return |
| 110 | |
| 111 | if addr < 0x8 or addr > 0x77: |
| 112 | raise I2cError('Error: invalid I2C slave address %s', addr) |
| 113 | |
| 114 | logging.info('Attempt to set slave address: %s', addr) |
| 115 | if not self.fd: |
| 116 | self.fd = self._getDeviceFile() |
| 117 | |
| 118 | ret = self.lib_obj.SetSlaveAddress(self.fd, addr) |
| 119 | if ret < 0: |
| 120 | raise I2cError('Error communicating to slave address %s' % addr) |
| 121 | |
| 122 | self.slave_addr = addr |
| 123 | logging.info('Slave address set to: %s', addr) |
| 124 | |
| 125 | def writeByte(self, reg, byte): |
| 126 | """Writes a byte to a specific register. |
| 127 | |
| 128 | TODO(tgao): add retry loop and raise error if all retries fail. |
| 129 | |
| 130 | Args: |
| 131 | reg: a (positive) integer, register number. |
| 132 | byte: a char (8-bit byte), value to write. |
| 133 | |
| 134 | Raises: |
| 135 | I2cError: if error writing byte to I2C bus. |
| 136 | """ |
| 137 | logging.info('Attempt to write byte %r to reg %r', byte, reg) |
| 138 | if self.lib_obj.WriteByte(self.fd, reg, byte) < 0: |
| 139 | raise I2cError('Error writing byte 0x%x to reg %r' % (byte, reg)) |
| 140 | |
| 141 | logging.info('Successfully wrote byte 0x%x to reg %r', byte, reg) |
| 142 | |
| 143 | def readByte(self, reg): |
| 144 | """Reads a byte from a specific register. |
| 145 | |
| 146 | TODO(tgao): add retry loop and raise error if all retries fail. |
| 147 | |
| 148 | Args: |
| 149 | reg: a (positive) integer, register number. |
| 150 | |
| 151 | Returns: |
| 152 | byte_read: a char (8-bit byte), value read from register. |
| 153 | |
| 154 | Raises: |
| 155 | I2cError: if error reading byte from I2C bus. |
| 156 | """ |
| 157 | logging.info('Attempt to read byte from register %r', reg) |
| 158 | byte_read = self.lib_obj.ReadByte(self.fd, reg) |
| 159 | if byte_read < 0: |
| 160 | raise I2cError('Error reading byte from reg %r' % reg) |
| 161 | |
| 162 | logging.info('Successfully read byte 0x%x from reg %r', |
| 163 | byte_read, reg) |
| 164 | return byte_read |
| 165 | |
| 166 | def writeWord(self, reg, word): |
| 167 | """Writes a word to a specific register. |
| 168 | |
| 169 | TODO(tgao): add retry loop and raise error if all retries fail. |
| 170 | |
| 171 | Args: |
| 172 | reg: a (positive) integer, register number. |
| 173 | word: a 16-bit unsigned integer, value to write. |
| 174 | |
| 175 | Raises: |
| 176 | I2cError: if error writing word to I2C bus. |
| 177 | """ |
| 178 | logging.info('Attempt to write word %r to reg %r', word, reg) |
| 179 | if self.lib_obj.WriteWord(self.fd, reg, ctypes.c_uint16(word)) < 0: |
| 180 | raise I2cError('Error writing word 0x%x to reg %r' % (word, reg)) |
| 181 | |
| 182 | logging.info('Successfully wrote word 0x%x to reg %r', |
| 183 | word, reg) |
| 184 | |
| 185 | def readWord(self, reg): |
| 186 | """Reads a word from a specific register. |
| 187 | |
| 188 | TODO(tgao): add retry loop and raise error if all retries fail. |
| 189 | |
| 190 | Args: |
| 191 | reg: a (positive) integer, register number. |
| 192 | |
| 193 | Returns: |
| 194 | a 16-bit unsigned integer, value read from register. |
| 195 | |
| 196 | Raises: |
| 197 | I2cError: if error reading word from I2C bus. |
| 198 | """ |
| 199 | logging.info('Attempt to read word from register %r', reg) |
| 200 | word_read = self.lib_obj.ReadWord(self.fd, reg) |
| 201 | if word_read < 0: |
| 202 | raise I2cError('Error reading word from reg %r' % reg) |
| 203 | |
| 204 | logging.info('Successfully read word 0x%x from reg %r', |
| 205 | word_read, reg) |
| 206 | return word_read |